I'm running a fairly simple pupillometry experiment, with fixation preceding stimulus to capture the baseline. I've been able to capture differences between my two conditions during the stimulus (for long presentations) and after stimulus (for short presentations)...but I have differences between conditions in the fixation before the stimulus even comes on. What could possibly be causing this? Trials are completely randomized, and yet these differences are consistent across participants.
Hey Steve!
Besides Luke's very good suggestions, I assume you controlled for eye movements (saccades and their preparation can affect pupil size).
In addition, anticipation does affect pupil diameter (and participants are generally very good in building up any sort of anticipation from only the tiniest clues). If your fixation periods were different or by chance longer in one condition than the other, this could also lead to a difference in pupil diameter.
Greetings, David
Hi Steve, Luke, David. You may be interested in this. A subjective account!
Vision-Space: Living without pictorial geometry: https://youtu.be/8sej-ueB6WQ
Abstract:
Fixation and saccadic eye movements take place within a field structure generated and controlled by the biological system. Both ‘generation’ and ‘control’ would appear to be dependent upon self-organising criticality (SOC) articulating the interface between how the data presents and the path along which the biological system has evolved in order to exploit this and so establish its ecological niche. These factors build to facilitate core capabilities determining the human umwelt.
Our perceptual processing system doesn’t map the environment through a series of pictures to provision spatial awareness or orientation. The only factors providing a coherent thread to visual experience are the processes governing fixation and saccadic eye movement made within a perceptually generated field structure. We see the world in relation to ourselves. To my mind, these processes are ultimately expressions of the same system, products of SOC revealing that dynamical systems run both the universe and hence perceptual awareness. It is through these processes that we develop our ability to model the external world. This identifies that perceptual modelling is not commensurate with the type of modelling that drives our current virtual reality and image making technologies.
In Vision-Space, reality and with that location, becomes a matter of judgment for the sentient being to realise, not measure. Location is a subjective construct and it has to be. Our current instrumentation is not designed to make these judgments or even to perform one of the necessary data-realisation procedures.
Only by studying vision as vision will we understand or keep connected to what’s actually involved in an act of observation.
Full list of Vision-Space presentations attached.
Best - John
In my research I found that differences in pupil size can be associated with sympathetic responses to sad faces within political orientation groups.
I essentially determined that when more conservative political moderates viewed sad faces, the range in overall pupil size within that group was greater, as well as the overall average size compared to that of political conservatives and liberals. The subjects did not self-identify by orientation or party. Political orientation in this case was determined arbitrarily according to a pre-screen survey and questionnaire regarding governmental policies.
My point is mainly this that when tested and compared on level of voluntary altruism and policy preferences, a more conservative sample (indeed these were University of Nebraska undergraduate students who by and large were raised in homes registered Republicans) tended to prefer less altruism when selecting support for various charities.
When the same population was tested on visual reactions to sad faces (not intended to be associated with either the prescreen survey or questiknnaire, the moderates who demonstrated markedly less altruism then the liberal orientation group, also matched or exceeded the lack of altruistic tendencies when compared to the more conservative portion of the sample.
In the interim, as I am still working on this I find that the difference in Baseline May in fact be attributable to more internal reasoning and greater interaction with affective relationships to attitude objects.
I think that although a larger Baseline pupil size indicates perhaps more calmness or less alarm. In the context of a political orientation group where feelings and meaningfulness reflect on the relevant political factors, a larger versus a smaller pupil size indicates a more extensive internal affect perhaps indicating subconscious moderating of feelings and cognition.
Sorry for the late response. You all had amazingly comprehensive answers. It turns out that the differences were just based in the noise of not having enough participants. Using a more validated baseline correction also helped :P
- Badges
- Science topic